Direction finder



Patented Mar. 29, 1949 DIRECTION FNDER Frank J. Lundburg, New York,Ni-Y, assignontm Federali'lelephone'and Radio@Corpmation;` New YorkgiN.Y., a corporation-of Delaware applicationMay-zs; 1945, serial No.596,143

5 Claiins. 1.

The present invention relates to direction nders; particularly of thephase comparisontype.

Certain types of direction iinders depend for their operation oncomparisons of the phase of 5 ofE which: are usuallyartiii'cial lines)and theA re-- ceiver iscoupledfat'variouspoints along said-lines.

If: the transmission lines are electrically 'lat,` that-ia, do notsupport standing Waves, andthe systemv is otherwise symmetrical, thenlthe voltages-at the electrical center of both transmission lines-willbeequal and; in phase when the trans-- mitter isequidistant from bothantenna units. When the transmitter is closer to one antenna unit. thantoanother, assuming the other con--` ditions are the same, the point atwhich the voltages will be; equal and in phase shifts toone side of thecenter of the transmission lines and the position of said point variesaccording to the lineof direction: to the` transmitter. Thus by locatingthepoints at which equalV and in-phase voltages are encountered on thetransmission line; anindication of the: line of directionto thektransmitter canY be obtained.

In` said systems;Y a. large proportion ofv thevl ener-gy received bytheantenna unitsl'is dissipated' in. the: terminations of theirtransmissionp lines.: lncertainityp'essuch asM. Fuchs-7, for"PhaseSeptember 11, 1944, this energy is dissipated in the o'tlferVA antennaunits' ofv the -pair usually 'in the formroff heat or reradiatedener-gy. Furthermore in` suoli receivers; it is impossible to keepthetransmission Vlines electrically flat despite the use* ofI matchingterminating resistances'- since the matching" is upset' by thel varyingamountof energy'drained'from'- t-he lines by the directionndingreceiveras' it isrcoupled to various' pointsalong saidl lines.

-are undesirable and lessen` the eiiiciency and accuracy of operation.

An' object oi the? present invention is the p'r-ovision of an improveddirectionv nder of the phase comparison type;

Another object ofthe present invention isfthe provision of adirectioninder ofY the phase comparisontypein which alrelatively smallamount of I These factors-the relatively f large lossl of energy andthelack` of flatness' of` the lines along which thephase is being measured2,. the' energy picked up by ther antenna-- systemisdissipatedbettveeni-the' antenna system andthe-f receiver;

Anetherrobject of the' present i-"nven'tioriv is'ftliel provisionf of aldirectionfinding receiver of the"l phase comparison Ltyp'e-iiiAwhichrthe transmission iinesialongwhichtnefphase coniparisonis made. aresubstantial-lg# electrically flat'.

Stili anotherob'iectfofl. my inventioniiszt-herprovision: of: a:-`directioni* nader: off the'- phase conr-4parisonfstypeidzwhichftnetransmission linesiuse'diy iori'determiningphase: relations: are-f connected -in-L auxiliary circuits instead ofthe: antenna: output;A circuits;

Xn'- accondance lwiitl'iffmyi invention; .signalienergyf' from. twoIspacedrand: separate antenna units.v isf applied. tol two'` separate;mixers or convertersa Energy: from: a local: oscillator isz alsorapplied: toi-f these mixers) but the .phaser ofl the: locali energy;applied 1 to? one-vofsaid mixers is adapted ltofbeinversely. Varied withrespect to therv phase ofthe" local energy; applied tothe other'ofsaid=mixerss Thesignal energyand thezlocal energyare mixed: infcach:mixer with the phases ofthezlocalienergy, being inversely varieduntiltheresultant-output energies of the mixers are equal and; inl phase. Bythencomparingy the: phase-off the locah energy applied* to-one mixerwithrespect. to '-thevphaSey of.' the; local! energyl applied.- tofthefother mixen,- an'- indicationmf thediierence'lnphase between thelincoming sig-nal: energies is' obtained; the lastv mentionedldifferencein i' phase'tindicating the' diL rect-ion line of-- the`transmitter.

Other-and'furtherr objects of' the mventlon' wllL become` apparent andithef` inventionJ willi bebest# understood from thefollowingidescription. ofi am embodiment thereon. reference-1 bein'gir had to'.the drawing in which.theisinglegurelis a schematicl andi block: diagraniof? a direction finder? embodyiing my invention.

Referring now' totliedrawing; sig-nal? energy from antenna units'- Iv'and 2 is"lv applied throgl transnissiontlne'sil and respectively-f totuned cir'miits"` 5: andf a respectively, the out-'put or. sarditunedicircuits-15 and iiloeingl fed ltir asymmetrical? conductorsordetectors'iy and? c *respectively which' detectors 'i and 8 serve* asmixers inA` the signal energy is mixed with energy from a lo'ca'lloscillator 9, the-tuning of: saidoscillator being ganged with the tuningof said circuits to produce` ing is a preferred form. The output of thel'o'caii' oscillator 9 is appl-ied'to'tihe *cent-er or midpoint C-J I otatransmissionl line- Ll termina-tingA inhits opposite ends in matchingterminating resistances I2 and I3 respectively. A pair of capacitivepick-ups which may be in the form of capacitive plates I4 and I5respectively are positioned on opposite sides of the center lil inassociation with the line I I, the energy picked up by plate I4 beingdelivered to mixer 'l while the energy picked up by plate I5 isdelivered to mixer 8. Plates I4 and I5 are mechanically linked togetheras indicated by line I6, and to a pointer I'I associated with a scaleI8.

If the transmission line I I is flat, it will be seen that the phasethereof varies symmetrically from the midpoint Ill toward the resistanceI2 and from the midpoint Ill toward the resistance I3. If the plates I4and I5 are moved in the direction of arrow I9, the phase of plate I5will approach the phase of the midpoint Iii, whereas the phase of plateI4 will move or shift away from said phase. The opposite is true if theplates I4 and I5 are moved in the direction of arrow 2i). It will thusbe seen that the phases applied through capacitive plates I4 and I5 tothe mixers I and 8 are varied inversely. The output of detectors 'I andare applied to the ends 2l and '22 respectively of the primary coils 23of a balanced transformer 24. The capacitive plates I4 and I5 are moveduntil the energy at end 2| of the primary 23 is equal in amplitude andis in phase with the energy at end 22. The resulting position of thepointer Il on the scale I8 then gives an indication of the directionfrom which energy is being received. As will be appreciated from areading of the aforementioned copending application of N. Marchand 7,the scale I 3 will be non-linear unless while the pointer I'I is movedlinearly over the scale the coupling plates I4 and I5 are moved as asinusoidal function of the linear movement in relation to thetransmission line II.

To determine when the energies at 2| and 22 are equal and in phase, thebalanced transformer 24 is tuned to the difference (or sum) of thesignal energy and the frequency of the local oscillator 9. The secondarycoils 25 of transformer 24 are connected to each other in parallel andto an intermediate frequency amplier and detector 2&5, the output ofsaid amplier and detector 26 being applied to a suitable indicator 2lwhich may be in the form of a milliammeter or the like. When theenergies at ends 2| and 22 of the primary 23 are equal and in phase noenergy will be delivered by the secondary to the amplifier and detector25 and the meter 2l' will indicate this.

In order for this system to operate properly, it should have electricalsymmetry at each side of the line 28-28. If the foregoing relationexists, then the received signal of frequency fp and amplitude E1 willbe applied to circuits 5 and 6 with the following phase relation, theinitial phase of the signal taken as zero:

Ei cos (21rpt-I-I-01l) At 6:

E1 COS (ZTrp-I-Hz) The local oscillator signal of frequency q andamplitude E2 will have the following phase relathe two detectors F and Gwill be assigned a square law characteristic and since the transformer Jis tuned to a frequency f=pq then a voltage will be developed from end2I to ground and end 22 to ground as follows:

At 2I to ground:

KEiEz cos (21rft-H1-I-0a) At 22 to ground:

KElEz COS (21rfZf-I-H2-l-04) where K is a constant having the dimensionsof conversion transconductance for detectors 'I and 8.

When (0s9i)=(02-Ie4)=6 the two voltages from 2l to ground and 22 toground will be equal in amplitude and phase. Connecting the secondary 25of the transformer 24 in a bucking a1'- rangement, zero signal voltagewill be applied to the intermediate amplifier and detector 2B giving asignal null when the above phase relation, 0, exists, Departure fromthis phase relation will produce a signal level at the input to 26.

By making the capacity between capacitive plate I4 and transmission lineII, and plate I 5 and transmission line I I as small as possible, verylittle of the signal energy will be transmitted by means of these platesI4 and I5 to be dissipated in the terminating resistances I 2 and I3. Atthe same time if such capacitances are small, the proportion of energytaken from transmission line I I and applied to the mixers 'I and 8,will be so slight that the line l I will remain substantiallyelectrically flat. By increasing the output of the local oscillator, itis possible to make these capacities very small and still provide enoughenergy for mixing in the detectors 'I and 8.

While I have described the details of one specific embodiment of myinvention, it will be apparent from the foregoing descrip-tion thatnumerous other embodiments differing from that illustrated may beconstructed utilizing my invention. For example, the indicator may be acathode ray oscillograph tube having a linear sweep, while thecapacitive plates I 4 and I5 are moved back and forth across thetransmission line Il as a harmonic function of said linear sweep, asdescribed more fully in the aforementioned copending application N.Marchand-7. Accordingly, while I have described above the principles ofmy invention in connection with specic apparatus, it is to be `clearlyunderstood that this description is made only by way of example and notas a limitation on the scope of my invention as defined in theaccompanying claims.

I claim:

l. A direction finder comprising a pair of mixers, a pair of spacedapart antenna units each coupled to separate ones of said mixers, alocal oscillator supplying energy to both of said mixers, means forvarying the phase of the energies supplied by said oscillator to one ofsaid mixers in relation to the phase of the energy supplied by saidoscillator to the other of said mixers, an indicator means controlled bythe outputs of said mixers, said phase varying means comprises atransmission line coupled at one end to the output of said oscillator, amatching resistive impedance terminating the other end of said line, acapacitive coupler adapted to be capacitively coupled to saidtransmission line at a selected one of a number of points on said line,and means for coupling said capacitive coupler to said one of saidmixers.

2. A direction finder comprising a pair of mixers, a pair of spacedapart antenna units each coupled to a separate one of said mixers, alocal oscillator supplying energy to both said mixers, means for varyingthe phase of said energy supplied by said oscillator to one of saidmixers While inversely varying the phase of said energy supplied by saidoscillator to the other of said mixers, and indicator means controlledby the outputs of said mixers, said phase varying means comprises atransmission line coupled at the midpoint thereof to the output of saidlocal oscillator, a pair of matching resistive impedances terminatingthe ends of said transmission line, a pair of capacitive couplersdisposed on opposite sides of said midpoint and each adapted to becoupled to a selected one of a number of points on the side of said lineWith which eacli of said couplers is associated, means for mc-ving saidcapacitive couplers inversely with respect to the midpoint of saidtransmission line, and means coupling each of said capacitive couplersto a separate one of said mixers.

3. A direction nder according to claim 1 wherein said indicator means isadapted to indicate when the outputs of said mixers are equal in phase,and said phase-Varying means is calibrated to indicate the relativephase of energy applied to the mixers.

4. A direction nder comprising a pair of mixers, a pair of spaced apartantenna units each coupled to a separate one of said mixers, a localoscillator supplying energy to both said mixers, means for Varying thephase of said energy supplied by said oscillator to one of said mixersin relation to the phase of said energy supplied by said oscillator tothe other of said mixers, said phase-varying means being calibrated toindicate the relative phases applied to said mixers, a balancedtransformer having each end of its primary connected to the output of aseparate one of said mixers, and an indicator coupled to the secondarycoils of said transformer.

5, A direction finder comprising a pair of mixer circuits and a pair ofspaced apart antenna units coupled to separate ones of said mixercircuits, a source of modulation signals, means for applying modulationsignals to each of said mixer circuits comprising separate terminatedtransmission lines, means for controlling the phase of said appliedmodulation signals comprising means for controlling the point ofcoupling between each of said transmission lines and said mixer circuitsand means for comparing the output of each of said mixer circuits toobtain a bearing indication of antenna received signals.

FRANK J. LUNDBURG.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,510,792 Merritt Oct. 7, 19241,839,290 Bailey Jan. 5, 1932 2,188,556 Nickel Jan. 30, 1940 2,275,254Falloon Mar. 3, 1942

